It is well known that power can be wirelessly conveyed from one place to another using the Faraday effect, whereby a changing magnetic field causes an electrical current to flow in an electrically isolated secondary circuit.
Such power transfer is reasonably efficient, given highly efficient coupling between the primary coil which creates the changing magnetic field and the secondary coil that is acted upon by the changing magnetic field. Normally, such coupling is achieved by placing the coils in extreme proximity to one another, but in some cases such placement may be impossible or undesirable. The coils' coupling efficiency can be reasonably high even without extreme proximity, if the coils resonate with a high Q at the same frequency—a phenomenon which has been applied in transdermal power supplies for biomedical implants and which is being investigated in relation to battery chargers for small appliances such as cellular telephones.
It is impractical for Q to be much greater than 100, and even in that case it is necessary to employ RF frequencies, which is of potential concern, due to the lack of long-term epidemiological studies of possible medical side effects associated with time-varying fields. Generally, there is strong evidence that low frequency magnetic fields are not harmful. It is accordingly desirable to achieve high power transmission efficiency at lower frequencies.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.